The effect of gestational age on neonatal outcome in low-risk singleton term deliveries

To assess the association between gestational age at delivery and adverse neonatal outcome among term low-risk singleton neonates.

A retrospective cohort study design was used. The study group included all low-risk singleton term (37 + 0 to 41 + 6 weeks) newborns delivered in a single tertiary university-affiliated medical center over a 5-year period. Outcome of neonates delivered at 37 + 0 to 37 + 6 weeks of gestation (early term) and 41 + 0 to 41 + 6 weeks of gestation (late term) was compared to that of neonates delivered at 39 + 0-39 + 6 weeks of gestation (control).

Overall, the outcome of 30 229 neonates was analyzed. The incidence of neonatal mortality was 1.0 per 1000 live-born neonates, with no significant difference between the various gestational age groups. Early term newborns were at higher risk for respiratory morbidity, hypoglycemia, hypocalcemia, thrombocytopenia and unexplained jaundice, and had higher rates of prolonged hospital stay, NICU admission, sepsis workup and antibiotic treatment. On multivariate analysis, early term delivery was an independent predictor for composite respiratory morbidity (OR=2.4, 95% CI 1.6-3.8, p < 0.001), unexplained jaundice (OR=2.1, 95% CI 1.7-2.5, p < 0.001), hypoglycemia (OR=2.5, 95% CI 1.5-4.3, p < 0.001) and NICU admission (OR=1.9, 95% CI 1.5-2.5, p < 0.001). Late term neonates had a significantly higher rate of large for gestational date, but did not differ from controls with respect to the rate of composite neurologic or respiratory complications, NICU admission, birth trauma or infectious morbidity.

Even in low-risk singleton deliveries, early term is associated with an increased risk of neonatal morbidity.